From an American perspective, Salem is the most famous due to a general American-centric view of history we tend to have here.

Salem also probably has in advantage in that we can reconstruct a lot of the details of the events. Simply put, a lot of the witch trials that took place elsewhere (especially in the early modern Holy Roman Empire) were extremely messy, chaotic, and left very little evidence. Thus, we have inexact numbers and at least one historian has hypothesized that many large witch trials might have escaped attention in general.

Why does very little evidence survive? Well, it's very possible that documents never existed in the first place. I'm going to use the Holy Roman Empire as an example since it's the location I'm most familiar with. In massive witch panics involving torture and many executions, the orderly legal code (the Carolina) more or less broke down. For a good idea of a "by the book" witch trial, check out The Trial of Temple Anneke (it might be out of print, but I got it on kindle a few years back). This is a wonderful source due to it's rarity and the fact that it was translated. The breakdown of the rules increased the likelihood that officials failed to write things down.

In saying this, I should acknowledge that I am relying primarily on my own reading of the documents. I wrote an original research paper about this in university. However, the public historiography appears to support this interpertation. While I am very proud of my work, I do acknowledge it has weaknesses including that I had to rely soley on translated materials and the only copy of the Carolina I could find (on a limited time scale) had some very important chunks missing. So, if there has been any counterarguments, please feel free to call my interpertation into dispute.

Another interesting book about early modern witch trials (Italy specifically) is The Night Battles. It's a bit of a doozy to read and can be rather confusing, but it's definitely worth it. I'd also recommend Brian Levack's work.